This invention relates to a fuse of the proximity-operating type, provided with a detonator the ignition of which is controlled by an electrical signal.
Fuses of this type normally comprise a proximity sensor device sensitive to electromagnetic waves which is able to emit an ignition signal for the detonator when the projectile on which the fuse is mounted is located at a predetermined distance from the target. Activation means, comprising for example an electronic switch, is normally disposed between the sensor device and the detonator, and is arranged to either make or break electrical connection between the sensor device and the detonator. This depends upon the presence or absence of an electrical activation signal emitted by a timer device which is arranged to emit the signal a predetermined time after launching the projectile. By controlling the activation means, trajectory safety is therefore attained such that any undesirable ignition of the detonator during the first portion of the trajectory, of any required length, is prevented. This length obviously depends on the time (or "lag") between the moment of launching and the moment of emission of the activation signal and this time can be set by adjusting the timer device.
In the fuses of the described type, in addition to the said electronic safety system, there are other systems of mechanical type, the purpose of which is to provide safety while the projectile traverses the firing mouth, or during an initial part of the trajectory. To obtain this further safety, the detonator is mounted on a rotatable member which can move it from a first position in which it is substantially non-aligned with the first element of the pyrotechnic chain and is therefore unable to transmit ignition to the chain, to a second position in which it is aligned with said first element and in which a terminal thereof is brought into contact with a contact element at which said ignition signal arrives. Said rotatable member is rotated by the centrifugal and inertia forces acting on the fuse, and is controlled by a delay device arranged to rotate the member in a predetermined "trajectory" time.
This second safety system therefore acts substantially in a mechanical manner, by retaining the detonator for a predetermined period of time in a position in which even if it were to become ignited, would not cause ignition of the pyrotechnic chain.